> More useful in a terminal emulator, however, is the ability to display the
> the official abbreviation [1,18], or "name", of the control character in a
> single cell. [...]
>
> Some control characters have two-character abbreviations (such as CR, LF,
> HT, FF), while others are three characters (NUL, SOH, DC1, DLE). Some
> terminals compress three-letter abbreviations to the two-character forms
> shown in Table 4.2. All terminals, however, display the abbreviations
> diagonally in the character cell, as shown in Figure 4.1. [...]
>
> Unicode already has a block of Control Pictures at U+2400 through U+2421,
> but (except for "NL" at U+2424) these go horizontally across the character
> cell, rather than diagonally, thus making them difficult to distinguish from
> normal alphanumeric text. A new, parallel block of C0 control pictures is
> needed in which the abbreviations are displayed diagonally.

This reflects a failure to understand the semantics of the
Control Pictures block, specifically the range U+2400 - U+214F,
which is documented on page 6-84 of the Unicode Standard 2.0.

# [F]or the control code graphics U+2400 -> U+241F only the
# semantic is encoded in the Unicode Standard. This allwos a particular
# application to use the graphic representation it prefers.
# [...] The [code points U+2400 to U+241F] are not associated with
# specific glyphs, but rather are available to encode <em>any</em>
# desired pictorial representation of the given control code.

The horizontal representations printed on page 7-188, therefore,
are not standardized in any way. Diagonal representations would
be entirely equivalent; the distinction is one of font only.